Relatives of a young boy who died with 54 injuries on his body are travelling to Westminster to lobby MPs for a change in the law.

Linda Terry, aunt of four-year-old John Smith, is campaigning for a new law to ensure guardians who kill children in their care are tried for murder.

John's adoptive parents Simon and Michelle McWilliam, from Southwick, are serving eight years for cruelty to the boy.

Murder charges against them were dropped last year because it could not be proved which, if either, delivered the fatal blow.

The Argus has been campaigning for a change since 2000 following the acquittal of a Brighton couple accused of smothering three babies.

The case collapsed because of the same legal stumbling block.

Mrs Terry, 41, from Pulborough, and John's grandfather James Sweeney, 72, from Hove, will visit the Houses of Parliament today to hand all MPs campaign leaflets.

Mrs Terry has sent 5,000 of the leaflets to supporters nationwide. The recipients sign their name on them and post them to Home Secretary David Blunkett.

Mrs Terry said: "I wrote to Mr Blunkett in July asking for his support but have not yet received an acknowledgement. It won't deter us. We will never give up or stop campaigning."

John's grandfather said he would carry on campaigning "for as long as I live to stop these killers hiding from justice."

He said: "It won't bring my boy back but we have to think of children in the future."

An NSPCC working party is holding a conference entitled "Which Of You Did It?" at Cambridge University next month before proposing changes to the law to the Home Office.